Paint stripping compositions are widely used industrial chemicals, and are used both in the finishing and refinishing of manufactured articles and in the clean-up of painting facilities. Significant amounts of paint-stripping compositions are used in connection with the refinishing of commercial and military aircraft, as well as the manufacture and refinishing of motor vehicles.
A threshold requirement for a good paint-stripping composition is that it efficiently and effectively removes a variety of paints without harming the underlying work piece. This requirement is particularly important in connection with the aircraft industry, since aircraft are frequently fabricated from lightweight aluminum or magnesium based alloys which are easily corroded by acidic or alkaline materials.
For a number of years, paint strippers based on methylene chloride were used because of methylene chloride""s effectiveness in quickly softening and undermining most types of paints. However, more recently the use of methylene chloride has become disfavored mainly due to its toxicity to humans and the environment. In addition, there is growing concern about the release of volatile organic compounds and hazardous air pollutants, such as methylene chloride, into the environment. As a consequence, regulations have strictly curtailed the amount of volatile organic compounds and/or hazardous air pollutants released into the environment. These restrictions are particularly important in their application to paint stripping compositions which are typically employed in relatively large volumes and distributed over large exposed areas.
As a consequence, there is need for paint-stripping compositions which have a low content of volatile and/or hazardous organic compounds but which can be effectively employed in a cost effective manner. It is particularly important for any proposed paint stripper composition be able to strip paint from a variety of substrates including steel, aluminum, magnesium and alloys of the foregoing without damage to the substrate.
In answering these needs a number of paint stripping compositions are known in the art. U.S. Pat. No. 5,990,062 to Summerfield, et al. discusses a paint stripping composition comprising benzyl alcohol, methylene chloride, hydrogen peroxide and water as well as a variety of optional secondary ingredients such as thickeners, surfactants, pH control agents, accelerators, corrosion inhibitors, preservatives, coloring agents and fragrances.
U.S. Pat. No. 6,030,466 to Myers discusses a paint stripping composition comprising tetrahydrofurfuryl alkyl ether, and a solvent selected from the group comprising of n-methyl pyrrolidone, glycol ethers, glycol ether esters, carbonates and mixtures of the foregoing along with a variety of secondary additives such as formic acid, corrosion inhibitors and fragrances.
U.S. Pat. No. 5,817,612 to Distaso discusses a paint stripping formulation comprising benzyl formate and a variety of secondary ingredients such as those suggested by Summerfield, et al. U.S. Pat. No. 5,851,972, also to Distaso, discusses a paint stripping product comprising benzyl alcohol and anisole. U.S. Pat. No. 6,025,313 to Weir also discusses benzyl alcohol based paint strippers.
U.S. Pat. Nos. 5,753,603 and 6,001,192, both to Lallier, et al., discuss paint stripping compositions based upon aprotic polar solvents such as n-methyl pyrrolidone. A variety of secondary ingredients are also discussed.
In accordance with the invention described herein, an improved paint stripping composition is disclosed which meets the needs described above. In particular, the composition described herein has been found to minimize the amount of volatile organic compounds and hazardous air pollutants while effectively and cost efficiently stripping paint from a variety of substrates, including steel, aluminum, magnesium and alloys of the foregoing, without damage to the substrate.
Disclosed herein is a paint stripping composition comprising an admixture of a solvent of the following molecular structure: 
with formic acid. A variety of secondary additives such as thickeners, surfactants, corrosion inhibitors, coloring agents and fragrances may also be added. Use of the foregoing composition in a method for stripping paint is also disclosed.
The present invention pertains to a paint stripping composition comprising an admixture of a solvent having the following formula: 
with formic acid, as well as a method for using the foregoing composition in a process for stripping paint from a variety of surfaces. The paint stripping composition of this invention may also preferably comprises thickeners, surfactants, corrosion inhibitors, coloring agents and fragrances. Most preferably, however, the paint stripping composition is substantially free of n-methyl-2-pyrrolidone. N-methyl-2-pyrrolidone is not required in this paint stripping composition, would add unnecessary cost, and would interfere with the stripping efficiency of the methyl benzoate and formic acid combination. As a result, it is recommended that the paint stripping composition of this invention be substantially free of n-methyl-2-pyrrolidone.
As noted, the paint stripping composition of this invention comprises methyl benzoate of the following structure: 
as a principal ingredient. The concentration of methyl benzoate in the paint stripping composition may range from 10 to 90 percent by weight of the paint stripping composition, but is preferably from 60 to 80 percent by weight of the composition. Methyl benzoate generally has a pleasant fragrance and therefore the paint stripping compositions of this invention can be used without odor objections and without the necessity of adding masking fragrances.
In addition to the foregoing methyl benzoate, this paint stripping composition also comprises formic acid. The concentration of formic acid in the paint stripping composition may range from 5 to 50 percent by weight of the paint stripping composition but is preferably from 15 to 30 percent by weight of the composition.
While the foregoing components provide a highly effective paint stripping composition, in many instances, auxiliary ingredients may also be used. Such auxiliary ingredients include thickeners, surfactants, corrosion inhibitors, coloring agents and fragrances.
Thickeners are widely used in paint stripping compositions primarily because they assist the stripping composition in clinging to the surfaces that are being stripped. Typical thickeners included fumed silica, various cellulose based materials such as methyl or ethyl cellulose and other known thickeners which are compatible with the ingredients of the paint stripping composition and which effectively thicken the composition and/or increase its viscosity. If thickeners are used, their concentration may range from 1 to 15 percent by weight of the paint stripping composition but will preferably be from 3 to 10 percent by weight of the composition.
Surfactants may also be used in order to improve the contact between the paint stripping composition and the surface being stripped. Non-ionic surfactants such as the Tergitol(copyright) series of surfactants available from the Union Carbide company are particularly useful. If used, the concentration of surfactant in the paint stripping composition may range from 0.5 to 5 percent by weight but is preferably from 1 to 3 percent by weight of the composition.
The paint stripping composition of this invention may also contain corrosion inhibitors for added protection of underlying metallic substrates. Such corrosion inhibitors may include triazoles, thiazoles, imidazoles, benzimidazoles and combinations of the foregoing. Preferred corrosion inhibitors include benzotriazole, tolyltriazole, mercaptobenzothiazole and other well known corrosion inhibitors. If corrosion inhibitors are employed, their concentration may range from 0.5 to 3 percent by weight of the paint stripping composition but is preferably from 1 to 2 percent by weight of the composition.
Although generally not functional, coloring agents or fragrances may be added to the paint stripping composition. As noted, since methyl benzoate has a generally pleasant fragrance, additional masking fragrances may not be necessary.
The paint stripping composition of the present invention is effective in stripping paints from a variety of substrates including steel, galvanized steel, zinc plated steel, magnesium alloys, aluminum and its alloys, and wood. This paint stripping composition has been found to be particularly useful in stripping paint from aluminum and aluminum alloys. A variety of paints are strippable with this formulation, including oil base alkyd and latex paints, varnishes, lacquers, shellacs, enamels, polyurethanes and epoxy coatings.
This paint stripping composition is generally applied at room temperature by spraying or brushing the composition onto the painted surface to be stripped. Stripping time may range from about 1 minute to 1 hour, depending upon the paint and particular surface conditions. Once the paint has appropriately lost adhesion from the substrate, the paint is removed by scraping, brushing or rinsing and then the surface is rinsed clean with an appropriate cleaner followed by water.